Method and apparatus for providing bubble-free liquid carbon dioxide

ABSTRACT

A method and apparatus for providing bubble-free liquid carbon dioxide to a user is disclosed. For cost-effective supply, gaseous CO 2  is removed from a supply line, liquefied in a condenser and transported to the user.

This application claims the priority of German Patent Document No. 10 2005 035 432.7, filed Jul. 28, 2005, the disclosure of which is expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a method and to a device for providing bubble-free liquid carbon dioxide.

While it is sometimes desirable to draw fluids with bubbles from a tank (beer, whipped cream), it is frequently desirable to provide the fluid bubble-free at the removal site or at the user's location. For example, when dosing or metering, it is important to keep the fluid pure in its liquid phase. The bubble-free drawing of gasoline allows exact metering. Likewise, when milk or other foaming foodstuffs are filled, care must be taken at all times that the desired filling amount is in fact put in the container. Inasmuch as, in most cases, dispensing is connected with a reduction in pressure, the risk of bubble formation increases as the liquid-gas phase boundary is approached.

Problems are posed by liquefied and/or cooled gases that, under normal conditions, always occur only in gaseous state. If, in addition, abnormal situations—as is the case with carbon dioxide, which, besides being known in the standard aggregate states of gas, liquid and solid, can exist in the states of super-critical and snow-shaped—are considered, there is currently no supply system that permits the reliable supply of only bubble-free liquid CO₂ at all times. Currently known supply systems consisting of a liquid CO₂ tank, a removal line for the liquid CO₂ and a valve upstream of the user, indeed supply liquid CO₂ but, when the stop valves are frequently opened and closed, a certain relaxation or warming upstream of the valve result in gas bubbles that could disrupt the operation by the user or the metering operation. In particular, considering expansion nozzles for the production of carbon dioxide snow or for cooling, liquid CO₂ should at all times be bubble-free upstream of the nozzle.

It has already been suggested (German Patent Application No. 10 2004 043912) to remove liquid CO₂ from a tank, to slightly heat the CO₂, cool it again and transport it in liquid state to the user. This form of supply has the disadvantage that it does not work at high external temperatures (above the critical point of the CO₂).

Considering the direct removal of fluid from a CO₂ bottle with a submerged pipe or from a cluster of CO₂ bottles with submerged pipes in the bottles, a portion of the fluid evaporates already in the removal hose or in the removal line, thus reducing the cleaning effect. Considering removal lines carrying liquid CO₂, each and every line segment that is separated by stop valves must be provided with safety valves. The gas must be safely exhausted to the outside. Large amounts of exhaust must be expected because the CO₂ in the line is present as a liquid. Therefore, this type of design is relatively complex and expensive.

Therefore, the object of the invention is to provide a supply device and a supply method that always provide bubble-free CO₂ in a more cost-effective manner.

Embodiments of the invention and devices for performing the method are disclosed herein.

It is characteristic of the invention that gaseous CO₂ is used to supply the user. This gas is transported through normal supply lines to the point of use. At the point of use or just before, the gaseous CO₂ is liquefied or condensed in accordance with the invention by cooling in a condenser. Then, the liquefied CO₂ is supplied to the user through a short feed line. As a result of the complete condensation and the subsequent sub-cooling of the CO₂, large amounts of CO₂ are produced during relaxation at the user end. Consequently, if the CO₂ snow is used for cleaning, the cleaning effect is increased significantly. It has been found that, in this way, the supply pressure may be below the normal CO₂ bottle pressure. Instead of a bottle pressure of approximately 50 bar, a line pressure of 10-30 bar is sufficient to achieve a good cleaning result.

In one embodiment of the invention, the CO₂ is sub-cooled in the condenser in order to avoid re-evaporation. In this case, sub-cooling may be minimal, i.e., 4-15° C., to reliably avoid re-evaporation before reaching the user.

The invention has the following advantages.

Complex and expensive fluid lines for the CO₂ supply are unnecessary. Existing CO₂ line systems with a gaseous product can be used. As a result of this, the costs for the condenser unit are more than offset and potential sub-cooling just upstream of the cleaning device ensures a reliable CO₂ reserve just prior to the “point of use.”

Safety is increased because the supply lines do not carry liquid CO₂.

The line between the condenser and the user should be as short as possible. Preferably, the line length is in the range between 100 and 300 cm. Also, the line may be insulated; however, this is not necessary when the flow rate is relatively high and the temperature difference is relatively minimal.

The method is particularly suitable when the user is a relaxation nozzle, because now, with the supply of always liquid carbon dioxide, a controlled operation of the relaxation nozzle is possible.

This is particularly advantageous when the relaxation nozzle is used for cleaning objects such as, for example, for cleaning welding nozzles such as MIG (metal inert gas) or MAG (metal active gas) burners. Splatters, particles or condensates, which need to be removed as quickly as possible in order not to seriously impair manufacturing cycle times, frequently adhere to these nozzles. Inasmuch as the cleaning process at times takes less than one second (0.5 second is recommended by the manufacturer), it is important to be able to provide the liquid phase from the start.

The current state of the art is described in the article “Schweissbrenner werden berührungslos gereinigt [Welding Burners are Cleaned in a Contactless Manner],” in Schweissen und Schneiden 56, issue 6/2004, p. 270. Indeed, this article mentions that CO₂ in ascending pipe bottles or tanks can be stored in liquid state under pressure; however, there is no description of any solution regarding how the CO₂ remains a bubble-free liquid from the tank to the device.

Similar methods have been known, for example, from International Publication No. WO 02/49794 A1; however, in this case the process does not use liquid CO₂ but CO₂ pellets and air.

Another application is the cooling of powders or substrates in thermal spraying (Linde brochure “Thermal spraying-controlled cooling with CO₂”).

A device for performing the inventive method comprises a supply container from which gaseous CO₂ is removed. By way of the supply line, the gaseous CO₂ is transported to a condenser that is located just upstream of the user and that liquefies and potentially sub-cools the CO₂.

The distance between the condenser and the user is as small as possible. Preferably, it is at 100 to 300 cm in order to ensure the mobility of the user, without requiring that the condenser must also be moved.

The CO₂ may be supplied either in a CO₂ bottle, by means of a cluster of CO₂ bottles or by means of a CO₂ tank, which contains the gas in liquid form, the gas then being brought into its gaseous phase by means of a separate evaporator. The gas can also be taken from an existing CO₂ line as is already available in many welding businesses. Considering all storage options, a pressure controller may be provided between the storage container and the supply line, should this be desirable.

Any common liquefier for CO₂ can be used as the condenser. Preferred is a condenser with an electrically operated refrigeration unit, because electrical current is available at virtually any workplace.

A particularly preferred user is a liquid CO₂ cleaning system, to which the CO₂ is supplied in liquid form. Considering this cleaning system, liquid CO₂ is relaxed in a nozzle having a valve, and then the snow/gas mixture is blown onto any object that is to be cleaned. For example, this object may be a MIG/MAG burner, from which welding spray residue needs to be removed.

BRIEF DESCRIPTION OF THE DRAWING

Referring to FIG. 1, one embodiment of the invention will be explained. In so doing, FIG. 1 shows the principle of supplying a user for cleaning welding nozzles.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 shows the upright CO₂ tank 1, in which liquid CO₂ is stored. An evaporator 2 can convert this fluid into its gaseous state. Alternative CO₂ storage options in this case are the CO₂ cluster 3 and the CO₂ bottle 4. Advantageously, if the supply occurs by way of an upright CO₂ tank, a low-pressure tank is used and, downstream of the evaporator 2, a unit for raising the pressure is provided. Each of the three storage options leads to a supply line 6, whereby a pressure controller 5 may be provided upstream of this supply line 6. The supply line 6 leads to condenser 8 in which the CO₂ is liquefied and then transported to the user by way of a CO₂ fluid line 9. The user, in this case, is the liquid CO₂ cleaning system 10 having a controllable valve and a relaxation nozzle. The supply line 6 may optionally supply other users by way of another line 7. In this case, for example, this is a welding operation. The CO₂, which has been relaxed in the relaxation nozzle, is directed at the welding burner, thus detaching adhering welding splatters due to temperature tensions and blowing them out with the gas stream. Referring to this embodiment, the liquid CO₂ cleaning system 10 is associated with a pressurized air supply line 11, from which pressurized air is optionally directed into the relaxation nozzle after CO₂ blasting. With the use of the additional pressurized air jet, the remaining welding splatters can be blown out without too much cooling of the burners.

Therefore, in accordance with the invention, the relatively long supply line 6 contains the CO₂ in gas form and is only liquefied in the condenser 8 shortly before reaching the user 10. In this instance, the CO₂ fluid line 9 is then relatively short. As a result, the otherwise relatively significant problems of providing liquid CO₂ carrying lines with options of venting to the environment have been avoided. Consequently, the total supply process is more cost-effective than conventional alternatives.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

1. A method of providing bubble-free liquid carbon dioxide to a user, wherein gaseous CO₂ is removed from a supply line, liquefied in a condenser and then transported to the user.
 2. The method of claim 1, wherein the CO₂ is sub-cooled in the condenser.
 3. The method of claim 1, wherein the liquefaction takes place just upstream of the user.
 4. The method of claim 1, wherein the CO₂ is used for cooling powders or substrates in thermal spraying.
 5. An apparatus for providing bubble-free liquid carbon dioxide to a user, comprising a supply line for gaseous CO₂ and a condenser for liquefaction just upstream of the user.
 6. The apparatus of claim 5, wherein a CO₂ fluid line between the condenser and the user has a length of between 100 and 300 cm.
 7. The apparatus of claim 5, wherein, for storing the CO₂, either a CO₂ bottle or a cluster of CO₂ bottles or a CO₂ fluid tank having an evaporator, is provided, and wherein a pressure controller is provided upstream of the supply line.
 8. The apparatus of claim 5, wherein the condenser is electrically operated.
 9. The apparatus of claim 5, wherein a relaxation nozzle is the user.
 10. The apparatus of claim 5, wherein the user is a liquid CO₂ cleaning system for objects, in particular, for welding nozzles such as MIG or MAG burners, MSG two-wire burners and/or laser hybrid burners.
 11. A method of providing bubble-free liquid carbon dioxide to a user device, comprising the steps of: removing CO₂ in a gas form from a supply line; liquefying the removed CO₂ gas from the supply line in a condenser; and transporting the liquefied CO₂ to the user device.
 12. The method of claim 11, further comprising the steps of: removing CO₂ in a liquid form from a CO₂ storage container; and converting the liquid CO₂ removed from the CO₂ storage container into the CO₂ in the gas form by an evaporator.
 13. The method of claim 12, further comprising the step of raising a pressure of the CO₂ in the gas form at a downstream location in a flow direction from the evaporator.
 14. The method of claim 11, wherein the step of transporting the liquefied CO₂ to the user device is performed with a fluid line that extends between the condenser and the user device.
 15. The method of claim 14, wherein the fluid line has a length which is substantially shorter than a length of the supply line.
 16. The method of claim 11, wherein the user device is a liquid CO₂ cleaning system.
 17. An apparatus for providing bubble-free liquid carbon dioxide to a user device, comprising: a supply line, wherein the supply line contains CO₂ in a gas form; a condenser coupled to the supply line, wherein the condenser liquefies CO₂ gas received from the supply line; and a fluid line disposed between the condenser and the user device, wherein the fluid line transports the liquefied CO₂ from the condenser to the user device.
 18. The apparatus of claim 17, wherein the user device is a liquid CO₂ cleaning system.
 19. The apparatus of claim 17, wherein the fluid line has a length which is substantially shorter than a length of the supply line.
 20. The apparatus of claim 17, further comprising: a CO₂ storage container, wherein the CO₂ storage container contains CO₂ in a liquid form; and an evaporator coupled to the CO₂ storage container and the supply line, wherein the evaporator converts liquid CO₂ received from the CO₂ storage container into the CO₂ in the gas form contained in the supply line. 